The use of chromium minerals in the 4th-3rd century BC China? A preliminary study of a bronze Pan unearthed from Jiuliandun Graves, Hubei Province, central southern China

A bronze Pan (water vessel), dating back to the 4th3rd century BC, was excavated at Jiuliandun in Hubei Province, central southern China, in 2002. The Pan attracts wide attention among the Chinese archaeologists and conservators for its uniqueness in style and color, which turns out to be due to a black-brown film of about 1 mm thickness. In the present work, a combined use of X-ray fluorescence (XRF), micro-Raman, and X-ray diffraction (XRD) was employed to determine both chemical and physical compositions of the Pan's film. The results are summarized as follows: (1) The film, as XRF analysis indicates, has high concentrations of chromium (Cr) and iron (Fe); (2) Both Raman and XRD analyses suggest that the element Cr probably exists in the film mainly in the form of chromium oxide (Cr2O3). Raman analysis also implies the presence of PbCrO4 . PbO in the film; (3) XRD analysis suggests that the element Fe exists in the film in the form ofmagnetite (Fe3O4). Based on these analytical results and Chinese historical records, we propose that, as early as in the 3rd century BC, people in central southern China might have discovered and intentionally used chromium minerals for bronze surface treatment (such as coating). The source of chromium minerals used in this period was likely Cr- spinel minerals from meteorites. More work remains to be done to test the possibility of using Cr- spinel minerals for bronze production and decoration. Other issues, such as the possibility of forming a chromium- rich film during the underground burial, also need to be solved. Copyright (C) 2011 John Wiley & Sons, Ltd.